1. Field Of The Invention
This invention relates to an accumulator charging system for a hydraulically operated rock drill.
2. Description of The Related Art
In a hydraulically operated rock drill kinetic energy of a reciprocating piston is converted to hydraulic energy on a return stroke and stored in one or more hydraulic accumulators by opening an operating valve as the piston moves to a limiting position.
The high pressure hydraulic fluid is passed through the valve behind the piston during the return stroke. The kinetic energy of the returning piston causes the pressure of the fluid to rise behind the piston and in a high pressure oil feed line.
The piston continues on its return stroke until the piston kinetic energy and the hydraulic energy are equalized. The kinetic energy is transformed to hydraulic energy which is stored in the hydraulic accumulator which is thereby charged with a certain volume of pressurized oil.
When the piston has fully retracted its kinetic energy is zero. At this point, on the high pressure hydraulic side, the constant flow of incoming pressurized oil and the charged accumulator contain substantial energy The accumulator has a charging area behind the piston which is the same as the accelerating area. As stated the accumulator is connected to the high pressure oil inlet side.
Problems encountered with the aforementioned arrangement include the following:
(a) generally the ratio between the percussive outlet power and the hydraulic inlet power is fairly low, for example of the order of from 0,55 to 0,65; PA1 (b) all the energy losses inside the rock drill turn to heat, thus raising the temperature of the rock drill and operating oil. The hot oil returning from the drill to a tank must be cooled before being pumped back to the drill. Oil cooling is a major problem, especially in a hot environment. If the temperature of the cooling air or water is close to the acceptable oil temperature, large coolers must be used. The cooling medium heats up the working environment; PA1 (c) large electric motors and hydraulic pumps must be used to supply sufficient operating energy to the rock drill. PA1 (d) The amount of electric power used for operating the rock drill is substantial and expensive.